set default away status to 'idle'

Starting with 98f3893 we support multiple awat statuses, that commit
changed the default away status to "online", resulting in commands like
'/away food' working the same way as 'set status food', i.e. leaving the
person in online state, but with a message set.
Change the default away status to 'idle' as it worked previously, this
should fix #161.

src/discord.c

@@ -289,8 +289,8 @@ static GList *discord_away_states(struct im_connection *ic)
 
     m = g_list_prepend(m, "invisible");
     m = g_list_prepend(m, "dnd");
-    m = g_list_prepend(m, "idle");
     m = g_list_prepend(m, "online");
+    m = g_list_prepend(m, "idle");
 
     return m;
 }